Vector kids is a great math site where kids can strengthen basic math as well as beginning algebra skils. It does not have many games but the ones they do are quality. Kids can practice these skills with timed flashcards (neat!), variable solving games,counting U.S. coins, geometric matching and math invaders.
*The Timed Flashcards and Variable Solving games have a high score board to gauge progress.
This site has math fact sheets, online practice opportunities, timed tests, It covers geometry, money, fractions as well. This is an excellent resource for primary teachers and for students to use at home.